Embodiments of the present invention are generally directed to surgical methods and are more particularly directed to controlling the flow of fluid to and from a patient through a fluid infusion and extraction system such as, for example, in ophthalmic surgery wherein surgical instruments such as electromechanical or pneumatically driven cutters as well as phacoemulsification instruments are commonly employed. These instruments require a source of fluid to infuse a surgical site and a source of negative pressure to evacuate the infused liquid and debris from the site. A pump is usually employed to generate negative pressure. Typical pumps are either flow pumps, such as, for example, peristaltic or scroll pumps, or vacuum pumps, such as, for example Venturi pumps, diaphragm pumps or rotary vane pumps.
A number of medically recognized techniques are utilized for cataractic lens removal based on, for example, phacoemulsification, mechanical cutting or destruction, laser treatments, water jet treatments, and so on.
The phacoemulsification method includes making a corneal incision and the insertion of a phacoemulsification handpiece which includes a needle that is ultrasonically driven in order to emulsify, or liquefy, the lens. Concomitantly, fluid is irrigated into the eye and the irrigation fluid and liquefied lens material are aspirated from the eye. Other medical techniques for removing cataractous lenses also typically include irrigating the eye and aspirating lens parts and other liquids. Additionally, some procedures may include irrigating the eye and aspirating the irrigating fluid without concomitant destruction, alteration or removal of the lens.
As is well known, for these various techniques it is necessary to maintain a stable volume of liquid in the anterior chamber of the eye and this is accomplished by irrigating fluid into the eye at the same rate as aspirating fluid and lens material. For example, see U.S. Pat. No. 5,700,240 which is incorporated herewith, in toto, by this specific reference thereto. FIG. 4 is similar to FIG. 1 of U.S. Pat. No. 5,700,240 and illustrates phacoemulsification system 60 including a control unit 62, indicated by the dashed lines in FIG. 4 which includes a variable speed peristaltic pump 64, which provides a vacuum source, a source of pulsed ultrasonic power 66, and a microprocessor computer 68 that provides control outputs to pump speed controller 70 and ultrasonic power level controller 72. A vacuum sensor 74 provides an input to computer 68 representing the vacuum level on the output side of peristaltic pump 64. Suitable venting is provided by vent 76. Also shown is eye 86, handpiece 80, irrigation fluid source 82, aspiration lines 88 and 90, irrigation line 84, ultrasonic power line 78, and output line 92.
During this procedure, it is possible for the aspirating phacoemulsification handpiece to become occluded. This occlusion is caused by particles blocking a lumen or tube in the aspirating handpiece. This blockage can result in increased vacuum (i.e. increasingly negative pressure) in the aspiration line and the longer the occlusion is in place the greater the vacuum. Once the occlusion is cleared, a resulting rush of fluid from the anterior chamber into the aspiration line can outpace the flow of new fluid into the eye from the irrigation source.
The resulting imbalance of incoming and outgoing fluid can create a phenomenon known as post-occlusion surge or fluidic surge, in which the structure of the anterior chamber moves rapidly as fluid is replaced. Such post-occlusion surge may lead to eye trauma. Current precautions against post-occlusion surge cause cataract surgery to be lengthier and more difficult for an attending surgeon.
Alternate surgical procedures, when an occlusion occurs, typically include a reduction of aspiration rate to a level less than the irrigation rate before continuing the procedure. This can be accomplished by changing the aspiration rate setting on the system. This, in turn, allows the pump to run slower and the fluid volume in the anterior chamber to normalize. Other alternate surgical systems may employ a restriction in the aspiration circuit to restrict surge flow when an occlusion clears from the aspiration tube.
Alternative techniques heretofore utilized include a reduction of vacuum on the occlusion by adjusting system settings. This technique often requires an assistant to perform the actual modification of settings.
Still another technique for vacuum control can be accomplished by reducing pressure on a control footpedal or releasing a footpedal altogether. This technique, however, requires a surgeon to discontinue applying ultrasonic power temporarily until the occlusion is either cleared or has been released from the aspirating phacoemulsification handpiece.
A disadvantage in releasing the footpedal is the fact that cataract lens material in the aspirating phacoemulsification handpiece may flow back into the eye chamber.
In addition, the combination of the hereinabove recited techniques may be employed as well. However, once an occlusion occurs, the surgeon must identify the cause and then take corrective action. However, the length of time before the occlusion clears varies. In the time it takes for a surgeon to identify the cause and request corrective action, the occlusion can build sufficient vacuum and then clear, thus resulting in post occlusion surge.
As a result, surgeons tend to operate their phacoemulsification systems at lower vacuum levels than otherwise preferable in order to avoid this problem. The present invention overcomes the disadvantages of operating surgical handpieces, as hereinabove identified.